Transistor amplifier circuit



March 8', 1960 FIG. 1l

o. L; MacsoRLEY r-:rAL 2,928,049v

TRANSISTOR AMPIIFIER CIRCUIT Filed sept. so, 1954 CURRENT A1?/ LIMITER Il l DRUM WRITE HEAD l l `|2 DRUM WRITE HEAD IN VEN TORS OLIN L'. MAC SORLEY BY HENRY4 E. COOLEY PEC/W ATTORNEY PVA.

United States Patent z,9,zs,o49 y rnnnsrsron Ammann cinemr n Olin L. MacSorley, Poughkeepsie, and Henry E. Cooley, Wappingers Falls, N .Y., assignors to International Business Machines Corporation, New York, N.Y., a corporation of New York l Appiisapnseptemper so, 1954, serial Ns.' 4s9,sss.

4 claims. (ci. .iso-zo sities or polarities. The magnetization of these areas'on the tape or drum is commonly carried out by an electromagnetic coil, the tape or drum being driven past theV coil, or writing head Vas. it is. called, whiley the coil is energized by an electric current cooled inV accordance with the data to be stored. Typically, the current in the coil consists of a series of pulses, which. are effectiveto produce on the tape or drum small magneti'zed areas having sharply defined boundaries. In order to utilize the storage capacity of a drum or tape to the utmost, it

Patentes Mss. s, 1960 connected in'parallel tol a common input terminal, and the output electrodes of the transistors are likewise connected in parallel to a common outputterminal. Each ofthe several parallel connected transistors is arranged asA an inverter circuit which is biased to cut off. The

emitter of each transistor is clamped to ground through a diode to 'prevent it fromA going more positive than ground.` A current limiting, resistor is connected' in each emitterY circuit so that each individual transistor output current andthe total' output current of the parallel transistorsV may be controlled.

,In one modification of the invention, the inputsignals are supplied to the.. transistors through a resistor-capacitor coupling, to insure sharp response, and` faithful following off thesquare wave forms. ln another moditlcationof the invention, a transfgnrmerY coupling'is used for the input signals to improvev operation at higher frequencies,V and to allow impedance matching wthgthe circuit which supplies signals to the amplifier. Y y

' Other objects and' advantagesr of the inventionwill become apparent 'fromV a consideration'V ofl the following specification and claims, taken togethery with the accompanying drawings. In the drawings:

4 Eigure l is aV wiringdiagrarn of an'- ampl' er circuit embodying the invention; randV '.flFigl-lre` 2 isl a, wiring diagram of another amplifier "circuit, ernb,odi/iu".I the invention.

is desirable to make these magnetized areas as small as possible. Forl that purpose, it is desirable to have the current pulses flowing'in. the coil repeated at a high frequency. Furthermoregsuch coils require substantial cur'- rents in order to produce magnetic fields of high inten- Sllly; Y l

Transistors have recently come into, use as translating and: amplifying devices.y in high speedk computers, being particularly suitable to that workV because of their low.

powerr requirements, in view-of the tremendous number, e-.g. many thousands, of such devices which are: required in complex computers. The useof transistor circuits in such` computers presents problems with respect to the energization of the. magnetizing coils of the data storage devices, because of the low current capacities of transistors, as comparedtothe coilv requirements, .and because of the low frequency and low voltagelimitations com,- mon in transistor circuits.

It has been proposed to operate transistors in parallel to supply heavier currents than can be handled by a singleI transistor. However, in conventional circuit arrangements, the divisionof load between parallel transistors is FIGURE l This figure illustrates a; circuit including threetransistors l which are connected in parallel. Theinventionjis not limited to the use of any specific, number of'transist'ors, three being chosen for convenience of illustration only. Each of the transistors l' andits associated circuit elements are equivalent toY their counterparts, so the same reference numerals have been used for all corresponding elements.

Eachtransistor l is a BNP junction transistor, having an emitter 1e,-V a oase lb and a collector lc. Emitter le. is connected through a resistor 2 to ay commonl junction vwire 3 leading to the positive terminal, of a. battery ll, whose negative terminalisconnectcd to ground. Base 1b is connected through a resistor 5 and a parallell capacitor 6 to a common junction wire 7 leading to a 'signal input terminal S. A. diode 91 is connected between emitter. le,

and ground., Collector lc is connected to. a common junction 10 andi thence through the coil ll of a` drum write headgenerally indicated at l2. to, thev negative. terA minal ofa battery t3, whosev opposite terminal is con:

" ,nected to ground, A; resistor 14 is. connectedv between determined by their internal resistances, with the result thaty 'one of two parallel transistorsl `may be overloaded,

whilev the other is supplying negligible current.

An object of the invention is to provide'a transistor amplifier circuit for supplying heavy currents.

' Another object-is to provide a transistor amplifier circuit4 including 'parallel connected'V transistors and meansV for controlling the division ofthe loadbetween the transis-tors. j'

A further object` is to provide a transistor amplifier circuit for supplyingsquare waves to a coil for magnetizinga data storage device. Y f

TheseA objects are attained in the circuits described herein, by connecting several transistors in parallel. In

other Words the input` terminals of the transistors` are.

base lb and' wire 3.

A 'square wave signal generator 25 is connected; be:

tween input terminal' 8 and ground. The generator 25 has a no signal potential of' 0 volts and a signal potential` of .8 volts.`

' OPERATION-FIGURE lV `Considering, first the operation of one of the transistors` alone, its emitter le is biased positively by theV batteryA t through resistor 2,n but it isclamped at groundpoten-.f

tial by the diode 9. In other words, the emitter; may

swing negatively with respect to ground, but it canv not;-`

swing positively. Baselb is biasedpositively withe re.-

spect to ground by battery 4 through resistor 14. The:

resistor i4. is chosen soI that base tb is just suliiciently positive to insure that the transistor is normally cut'` ofi. The no-signal conditional the input terminal 8 isy 0 volts, or ground potential. it may be seenA that the re;-

-V e sistors14 and 5 form a voltage divider suppliedby the battery l under no signal conditionsand that the values selected for resistors lll and 5 establishv the; potential-1 of base 1b.

When a signal is received at inputztcrrninal Spits-.poe

3 ,t tential drops to -8 volts, swinging the base 1b negative With respect to ground and turning the transistor on.

The saine response occurs at all three of the transistors in parallel, so that when an input signal is received at terminal S, the output currents of all three transistors are delivered through junction itl to the coil l1.

When any transistor is conductive, the resistor 2 connected in series with its emitter serves as a current limiting resistor. Specifically, as the emitter current goes up, a potential drop occurs across resistor 2 which tends to Swing emitter le increasingly in a negative direction. Eventually, the emitter le will be shifted to a potential sufficiently negative that a further change in that direction will start decreasing the current tlow through the transistor. The current limit has then been reached. By properly selecting the current limiting resistors, the maximum output current for the individual transistors can be determined, so that the current in the coil lll can be supplied in accordance with the requirements of the drum write head l2. For example, in the circuit illustrated, each transistor will supply approximately 16 ma. making a total of approximately 48 ma. for the three transistors. Furthermore, the division of the total load among the several transistors may be established independently of the internal impedances of the transistors.` Consequently, the load may be evenly divided, with none overloaded, and with each -contributing a share.

The diode 9 which grounds the emitter 1e has low forward resistance, and a quick recovery characteristic. When the transistor is conducting current, the emitter becomes negative with respect to ground, which causes the diode to enter its high resistance state, and the current which was formerly going through the diode goes through the transistor. When the input signal 3 cuts off, the transistor stops conducting, the emitter voltage rises toward +45, and is caught by the diode at ground. When the emitter le is at ground potential, the transistor is then immediately sensitive to another input signal.

FIGURE 2 Y winding 19 having its upper terminal connected to the base 1b of all three of the transistors. A battery 2t) suplies a voltage divider including resistors 21 and 22. The lower terminal of secondary winding 19 is connected to the junction 23 between resistors 2l and 22.

OPERATION-FIGURE 2 Under no signal conditions, the bias potential, taken from the junction .23 in the voltage divider circuit, is elective to hold the base 1b positive with respect to ground. The emitters 1e are clamped at ground potential by the diodes 9, so that the transistors are cut off. When an input signal is received in terminals l5 and 16, the polarity of the secondary winding i9 is arranged so that its upper terminal then becomes 8 volts negative with respect to its lower terminal. This potential is etfective to swing bases 1b negative and turn the transistors l on.

As in the case of Figure l, the resistors 2 operate to limit thevcurrent flow through the respective transistors. Also, as in Figure l, the diodes 9 insure a quick recovery of. the transistors after the passage of a signal.

While PNP junction transistors have been shown, it will be recognized that NPN transistors could be used with equal facility by reversing the polarity on all the batteries, and making other changes Well understood by those skilled in the art.

The following table shows by way of example particular values for the potentials of the various batteries and for the impedances of the various resistors and capacitors, in circuits which have been operated successfully. In some cases, the values are also shown in the drawing. These values are set forth by way of example, and the invention is not limited to them nor to any of them. The diodes are considered to have substantially no impedance in their forward direction, and substantially infinite impedance in their reverse direction.

Table 1 l Resistor 2 ohms 3K Battery t volts..- 45 Resistor S ohms 10K Capacitor 6 mfd 680 Battery 13 volts 15 Resistor 14 ohms.` 330K Battery 243 volts 45 Resistor 21 ohms 4.7K Resistor 22 do 100 While we have shown and described certain preferred embodiments of our invention, other modifications thereof Will readily occur to those skilled in the art, and We therefore intend our invention to be limited only by the appended claims.

We claim:

l. An amplier comprising a plurality of transistors, each having a common electrode, an input electrode, and an output electrode, a plurality of current limiting resistors, one for each transistor, means connecting the respective resistors in series with the common electrodes of their associated transistors, input circuit means including said resistors and connecting means and connected to the input electrodes, said input circuit means comprising a source of biasing potential tending to maintain a reverse bias between the common and input electrodes of all the transistors and signal input means providing a signal varying between a no-signal condition in which all the transistors are held cut 01T by the biasing source and a signal condition effective to overcome the biasing source and cause a substantial ow of current in all the transistors, output circuit means including said resistors and connecting means, said output circuit means connecting the output electrodes together and in series with a load device and a source of unidirectional electrical energy, said current limiting resistors having resistances effective when the transistors are conducting current to ensure a division among the transistors of the current ow through the load device.

2. An amplifier as dened in claim l, in which the input circuit means and the output circuit means connect a rst junction to the `terminals of the resistors remote from their associated common electrodes, and said output circuit means connects a second junction to the terminal of the series-connected load device and energy source remote from the output electrodes, said input circuit means including means connecting vthe biasing potential source between said rst and second junctions, and means connecting the signal input means between said second junction and a third junction, said input circuit means further comprising, for each transistor, two resistors connected in series between the first and third junctions, and a connection between the common terminal of the two resistors and the input electrode of the associated transistor; and also including, for each transistor, a capacitor connected between the input electrode and said third junction.

3. An ampiier as defined in claim 1, in which the input circuit means and the output circuit means connect a iirst junction to the terminals of the resistors remote from their associated common electrodes, and the output circuit means connects a second junction to the terminal of the series-connected load device and energy source remote from the output electrodes, said input circuit means comprising a single voltage divider serving all said transistors and comprising two resistors connected in series across said potential source, a connection between one terminal of the potential source and said second junction, a connection between the common terminal of the two resistors and o ne terminal of the signal input means, and a connection between the other terminal of the signal input means and all the input electrodes in parallel.

4. An amplifier as defined in claim 1, in which said input circuit means and said output circuit means connect a rst junction to the terminals of the resistors remote from their associated common electrodes, said output circuit means connects at least a portion of said source of energy between said first junction and ka second junction, and a pluralityr of diodes, one Vfor each transistor,

connected between said second junction and the common;

electrode of the associatedY transistor, said diodes being poled forwardly to current from `said portion ofV the v source, so thatcurrent ows continuously from said source portion through said'resistors, and isswitched between Y the diodes and the common electrodes by operation of said signal input means.

.K 6 i References Cited in the file of this patent UNITED STATES PATENTS 1,550,684 Espenshied Aug. 25,. 1925 2,535,912 Frank et al. Dec. 26, 1950v 2,612,567 Stuetzer Sept. 30, 1952 2,646,472 Rockwell July 21, 1953 2,647,958 Barney` f Aug. 4, 1953 2,655,610 Ebers Oct. 13,"1953 2,666,818 Shockley Jan. 19, 1954 l2,680,160 Yaeger June 1, 1954 l 2,717,931 Duke f.. Sept. 13, 1955 2,759,052 Macdonald et al. Aug. 14, 1956 2,760,087 Felker Aug. 21, 1956 OTHER REFERENCES Article in Electronics,September 1948, page 69. Y Shea text, Principles of Transistor Circuits, pp. 148- 149, pub. 1953` by John Wiley & Sons, N.Y.

Korn: Electronic Analog Computers, page 177, copy right 1952.

UNITED STATES PATENT OFFICE v CERTIFICATE OF CORRECTION Patent Nou 2,928,049 March 8v 1960 Olin L., Mac'Sorley et al.,

It is hereby certified that error appears in the printed specification of 'the above numbered patent requiring correction and that Jshe said Letters Patent should -readas corrected below.

Column 1 line 30o for "cooled" read' coded Signed and sealed this 18th day of ,October 1960.5,

(SEAL) Attest:

KARL H, AXLINE ROBERT C. WATSON Attesting Ocer Commissioner of Patents 

